The present invention relates to a configuration measuring apparatus and method, and particularly to an apparatus and method for measuring a surface shape of a thin plate member such as a wafer for manufacturing a semiconductor, in which little shape variation is required in a surface direction.
The wafer for manufacturing the semiconductor is constituted by a thin plate member such as a silicone wafer or the like. In order to form a semiconductor device or a circuit on a wafer surface, a photo engraving technique, a printing technique, various kinds of micro-fabrication techniques or the like is applied.
On the wafer to which such a working process is applied, it is important to increase a flatness of a surface. When flatness of the wafer is deteriorated, a pattern of the device or the circuit is unclearly formed, or a profile of a material to be printed onto the wafer surface in a pattern shape becomes indefinite, at a time of photo engraving. In particular, as a densification or a large-size of the semiconductor device or the circuit is promoted, the problem mentioned above becomes significant.
During a semiconductor manufacturing step, various kinds of processes are frequently executed in a state in which an entire surface of the wafer is supported in a closely contacted manner to a flat supporting surface by vacuum adsorption or the like. At this time, in a case that a thickness of the wafer has a dispersion, the dispersion of the thickness appears as a dispersion of the flatness of the wafer surface as it is at a time of supporting the wafer by the flat supporting surface in a closely contacted manner.
Accordingly, it is required that the dispersion or the variation in correspondence to this place is not generated in the thickness of the wafer. In order to estimate whether or not thickness variation of a manufactured wafer is large during a manufacturing step of the wafer or the like, it is necessary to accurately and efficiently measure the thickness variation of the wafer.
As a conventional wafer thickness variation measuring method, there is a technique described in Japanese Patent Application Laid-Open No. 2000-283728. With this technique, a displacement of wafer surfaces with respect to optical sensors arranged on side portions of both surfaces of a disc-like wafer is determined while rotating the wafer in a perpendicularly oriented state, whereby a magnitude of thickness variation of the wafer is calculated from the displacement of the wafer surfaces measured by the optical sensors. Scanning the wafer in a radial direction thereof by the optical sensors attains measurement of the thickness variation with respect to entire surfaces of the wafer.
The conventional wafer thickness variation measuring apparatus mentioned above has a limit in accuracy of measuring thickness variation, so that the apparatus cannot achieve measuring of the thickness variation with high accuracy required for manufacturing a semiconductor device or a circuit having high accuracy and density in the future.
In an optical displacement gauge used in the measuring apparatus, a change of distance between a respective one of the optical sensors and the wafer generates a interference signal of a sine wave shape with a cycle that is one half of a wavelength λ of a laser beam. In order to maintain a standard length and a traceability regulated in ISO, a frequency stabilized He—Ne laser having a wavelength of about 633 nm is used as a laser beam for measurement. In order to execute the measurement in accordance with the method mentioned above, an intensity of the sine-wave interference signal is detected in an analog manner, and a distance within a wavelength of μ/2 is detected by performing a computation.
However, since the sine-wave interference signal is generated by utilizing a polarization property of light, the interference signal has a slight shift with respect to an ideal sine-wave waveform due to a significantly little polarized light leakage or the like, in an optical part such as a μ/4 wavelength plate, or the like, used in a conventional optical displacement gauge, thereby generating an error in measuring a distance.
In correspondence to that density of a semiconductor device or circuit has become higher recently, a measurement of wafer thickness variation at an accuracy of not less than 0.0015 μm will be required in the near future. Owing to the measurement-principle thereof, such highly accurate thickness variation measurement as mentioned above is hardly possible. In a conventional optical sensor, an accuracy of about 0.003 μm is a limit.
Besides a wafer for manufacturing the semiconductor device, there are technical fields in which a significantly high accuracy in measurement of thickness variation is required, such as a substrate for a magnetic disc.
Therefore, an object of the present invention is to attain measurement of a thickness variation of a thin plate, such as a wafer, with high accuracy and high efficiency.